Search results for "SPECTRA"
showing 10 items of 3542 documents
Tripoxyrollin, a New Epoxy Acetogenin from the Seeds ofRollinia membranacea1
1993
Abstract A new epoxy acetogenin, tripoxyrollin (1), has been isolated from the seeds of the Colombian Annonaceae, Rollinia membranacea. Its structure was elucidated on the basis of spectral data. Biomimetic synthesis of isodesacetyluvaricin (2) from tripoxyrollin (1) suggests its key role in the biogenesis of the adjacent bis-tetrahydrofuran acetogenins.
The Hot Bands of Methane between 5 and 10 μm
1996
Experimental line intensities of 1727 transitions arising from nine hot bands in the pentad-dyad system of methane are fitted to first and second order using the effective dipole moment expansion in the polyad scheme. The observed bands are nu3 - nu2, nu3 - nu4, nu1 - nu2, nu1 - nu4, 2nu4 - nu4, nu2 + nu4 - nu2, nu2 + nu4 - nu4, 2nu2 - nu2, and 2nu2 - nu4, and the intensities are obtained from long-path spectra recorded with the Fourier transform spectrometer located at Kitt Peak National Observatory. For the second order model, some of the 27 intensity parameters are not linearly independent, and so two methods (extrapolation and effective parameters) are proposed to model the intensities …
Pulsations in the late-type Be star HD 50 209 detected by CoRoT
2009
The presence of pulsations in late-type Be stars is still a matter of controversy. It constitutes an important issue to establish the relationship between non-radial pulsations and the mass-loss mechanism in Be stars. To contribute to this discussion, we analyse the photometric time series of the B8IVe star HD 50209 observed by the CoRoT mission in the seismology field. We use standard Fourier techniques and linear and non-linear least squares fitting methods to analyse the CoRoT light curve. In addition, we applied detailed modelling of high-resolution spectra to obtain the fundamental physical parameters of the star. We have found four frequencies which correspond to gravity modes with az…
HADES RV Programme with HARPS-N at TNG. IV. Time resolved analysis of the Ca II H&K and Hα chromospheric emission of low-activity early-type M dwarfs
2016
Context. M dwarfs are prime targets for current and future planet search programs, particularly those focused on the detection and characterization of rocky planets in the habitable zone. In this context, understanding their magnetic activity is important for two main reasons: it affects our ability to detect small planets and it plays a key role in the characterization of the stellar environment. Aims: We analyze observations of the Ca II H&K and Hα lines as diagnostics of chromospheric activity for low-activity early-type M dwarfs. Methods: We analyze the time series of spectra of 71 early-type M dwarfs collected in the framework of the HADES project for planet search purposes. The HARPS-…
The early B-type star Rho Oph A is an X-ray lighthouse
2017
We present the results of a 140 ks XMM-Newton observation of the B2 star $\rho$ Ophiuchi A. The star has exhibited strong X-ray variability: a cusp-shaped increase of rate, similar to that which we partially observed in 2013, and a bright flare. These events are separated in time by about 104 ks, which likely corresponds to the rotational period of the star (1.2 days). Time resolved spectroscopy of the X-ray spectra shows that the first event is caused by an increase of the plasma emission measure, while the second increase of rate is a major flare with temperatures in excess of 60 MK ($kT\sim5$ keV). From the analysis of its rise, we infer a magnetic field of $\ge300$ G and a size of the f…
Improved centrifugal and hyperfine analysis of ND2H and NH2D and its application to the spectral line survey of L1544
2021
Abstract Quantifying molecular abundances of astrochemical species is a key step towards the understanding of the chemistry occurring in the interstellar medium. This process requires a profound knowledge of the molecular energy levels, including their structure resulting from weak interactions between nuclear spins and the molecular rotation. With the aim of increasing the quality of spectral line catalogs for the singly- and doubly-deuterated ammonia (NH2D and ND2H), we have revised their rotational spectra by observing many hyperfine-resolved lines and more accurate high-frequency transitions. The measurements have been performed in the submillimeter-wave region (265–1565 GHz) using a fr…
Study of a plasma generated in metal surface treatment by laser ablation in air : characterisations of induced radiation and nanoparticules
2015
The interaction of a laser beam of short pulse duration with metallic materials such as aluminum, iron or titanium is characterized by the presence of a high energy and strongly ionized plume (plasma). The aim of this study is to understand the mechanisms involved in plasma, created when laser-target interaction, which lead to the formation of nanoparticles. We would generally consider the dynamic expansion in the air of the plasma plume formed with a nanosecond Nd:YAG laser to specify the conditions of formation of these particles and their morphological and structural characteristics. Thus, this work is divided onto two parts. In the first part, we present the experimental characterizatio…
Collisional shifting and broadening coefficients for the rovibrational anisotropic S(J) lines of nitrogen studied by inverse Raman spectroscopy
1996
0377-0486; Line shifting and broadening coefficients of the anisotropic S(J) lines (v = 0, J --> v = 1, J + 2) of the nitrogen molecule were measured at room temperature using high-resolution stimulated Raman spectroscopy. A rotational quantum number dependence of the S(J) line shifts was observed. In order to avoid an asymmetry of experimental origin, a suitable theoretical profile was fitted to the experimental lineshapes. This study allows the testing of the theoretical methods for calculating the line broadening coefficients in anisotropic Raman scattering, which have already been used in the analysis of infrared absorption data. The behaviour of the modified sum rule and the RPA (rando…
Radioluminescence, thermoluminescence and dosimetric properties of ZnO ceramics
2017
The authors gratefully acknowledge the financial support for this work from research grant ERA.NET RUS Plus Nr.609556 and from the SFERA II project Transnational Access activities (EU 7th Framework Programme Grant Agreement no 312643) for supporting ZnO nanopowders preparation.
Estimation of actual evapotranspiration of Mediterranean perennial crops by means of remote-sensing based surface energy balance models
2009
Abstract. Actual evapotranspiration from typical Mediterranean crops has been assessed in a Sicilian study area by using surface energy balance (SEB) and soil-water balance models. Both modelling approaches use remotely sensed data to estimate evapotranspiration fluxes in a spatially distributed way. The first approach exploits visible (VIS), near-infrared (NIR) and thermal (TIR) observations to solve the surface energy balance equation whereas the soil-water balance model uses only VIS-NIR data to detect the spatial variability of crop parameters. Considering that the study area is characterized by typical spatially sparse Mediterranean vegetation, i.e. olive, citrus and vineyards, alterna…